Abstract
Abstract In the course of analysing the annual air temperature in Wrocław (TWr), a rapid change of the thermal regime was found between 1987 and 1989. TWr increased by >1°C, a strong, statistically significant positive trend emerged. The analysis of processes showed that strong warming in the cold season of the year (December–March) occurred as a result of an increase in the NAO intensity and warming in the warm season because of increased sunshine duration in Wrocław (ShWr). Multiple regression analysis has shown that the winter NAO Hurrell's index explains 15% of TWr variance, and the ShWr of the long-day (April–August) period 49%, whereas radiative forcing 5.9%. This indicates that the factors incidental to the internal variability of the climate system explain 64% of the TWr variability and the effect of increased CO2 concentration only ~6%. The reason for this rapid change of the thermal regime was a radical change in macro-circulation conditions in the Atlantic-European circular sector, which took place between 1988 and 1989. The heat, which is the cause of warming in Wrocław, comes from an increase in solar energy inflow (April–August) and also is transported to Europe from the North Atlantic surface by atmospheric circulation (NAO). These results indicate that the role of CO2 in shaping the contemporary temperature increase is overestimated, whereas the internal variability of the climate system is underestimated.
Highlights
Introduction and the purpose of researchThe air temperature in the Baltic Sea Basin and Central Europe, including Poland, has been growing rapidly and strongly over the last half century (Brázdil et al 1996, Fortuniak et al 2001, Kożuchowski, Żmudzka 2001, BACC 2008, Philipona et al 2009, Wójcik, Miętus 2014)
These results indicate that the role of CO2 in shaping the contemporary temperature increase is overestimated, whereas the internal variability of the climate system is underestimated
This study aims to assess the role of internal variability of the climate system in shaping the variability of temperature in Wrocław (TWr), a city with long-term meteorological observations
Summary
The air temperature in the Baltic Sea Basin and Central Europe, including Poland, has been growing rapidly and strongly over the last half century (Brázdil et al 1996, Fortuniak et al 2001, Kożuchowski, Żmudzka 2001, BACC 2008, Philipona et al 2009, Wójcik, Miętus 2014). Temperature changes in Wrocław in the years 1951–2018 are very strongly correlated with changes in annual temperature at stations in Poland (correlation coefficients r from 0.81 to 0.97) and at stations located in Germany, Austria, the Czech Republic and Slovakia, less strongly but significantly with air temperature at stations located in Denmark, southern Sweden, Lithuania, Belarus and Ukraine. This proves that the temperature increase observed in Wrocław is not a local phenomenon but a manifestation of a process of supra-regional scale. The contribution of natural intrinsic climate variability is assessed modestly in the latest Report
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